The present invention relates to a coated optical fiber, an optical fiber ribbon, and an optical fiber unit.
An optical fiber is obtained by drawing an optical fiber preform having at least a core and a cladding. Immediately after drawing, a coating is formed around the outside of the glass optical fiber in order to protect and reinforce the fiber and to give it flexibility, and for other purposes. It is known to form at least two layered coatings, namely, a relatively soft (low Young""s modulus) primary coating which is in contact with the outer circumference of the glass optical fiber and which has a buffering function, and a hard (high Young""s modulus) secondary coating formed on the outermost side and having a protective function.
For example, a coated optical fiber is proposed in Japanese Patent Application Laid open No. 9-5587, in which, by setting the extraction force (the force necessary to pull a glass optical fiber out of the coated optical fiber which is fixed from the outside), which force serves as the adhesion between the glass optical fiber and the primary coating material forming the primary coating, at 90 g/mm to 180 g/mm, an adequate adhesion between the glass optical fiber and the primary coating material is obtained, and partial delamination will not occur at the interface between the glass optical fiber and the primary coating material even when they are soaked in water for a long period.
However, when the extraction force corresponding to the adhesion between the glass optical fiber and the primary coating material is set at 90 g/mm to 180 g/mm as described in the above publication, delamination sometimes occurs at the interface between the glass and the coating material in the coated optical fiber during or after the production of the coated optical fiber: for example, during the period from drawing to cabling of the optical fiber or during winding onto another bobbin. It is thought that minute foreign materials such as chips of the optical fiber, adhering onto a pulley, on which the coated optical fiber travels, due to static electricity or the like cause the coated optical fiber to undergo large local deformation, and as a result, delamination occurs at the interface between the glass optical fiber and the primary coating.
An object of the present invention is to provide a coated optical fiber in which such delamination during the period from drawing to cabling is prevented.
A tapelike (ribbonlike) cable, which is formed by placing a plurality of coated optical fibers in parallel in a plane and by forming a unitary jacket around the coated optical fibers so as to coat them therein, is referred to as an xe2x80x9coptical fiber ribbonxe2x80x9d. When connecting optical fiber ribbons, it is necessary to collectively remove the layers: the primary coating formed around the outside of the glass optical fiber, and the unitary jacket. This operation is referred to as xe2x80x9ccollective stripping of coatingsxe2x80x9d. In this case, it is undesirable that the coatings such as the primary coating or secondary or other coatings remain on the surface of the glass optical fiber.
Another object of the present invention is to provide a coated optical fiber which has an improved delamination resistance during drawing and rewinding and whose collective strippability of coatings is not degraded when it is used as a component of an optical fiber ribbon.
A further object of the present invention is to provide a coated optical fiber which is assembled into a certain type of optical fiber unit or inserted into a loose tube and is subjected to stripping of individual coated fiber when connection is performed and in which the delamination resistance is increased and stripping of individual coated fiber is easy.
A still further object of the present invention is to provide an optical fiber ribbon in which the delamination resistance is increased and the collective stripping of coatings is easy, or an optical fiber unit in which the delamination resistance is increased and stripping of individual coated fiber is easy.
In order to achieve the above objects, the present invention relates to:
(1) A coated optical fiber having at least one coating formed around the outside of a glass optical fiber, wherein the storage modulus Exe2x80x2 of the primary coating in contact with the glass optical fiber is within the range of 0.01 kg/mm2 to 2.0 kg/mm2 at 25xc2x0 C. and 110 Hz, and the adhesion between the glass optical fiber and the primary coating is within the range of 10 g/cm to 200 g/cm.
(2) A coated optical fiber according to (1) above, wherein the storage modulus Exe2x80x2 is within the range of 0.01 kg/mm2 to 0.5 kg/ mm2 and the adhesion is within the range of 10 g/cm to 100 g/cm.
(3) A coated optical fiber according to (1) above, wherein the storage modulus Exe2x80x2 is within the range of 0.01 kg/mm2 to 2.0 kg/mm2 and the adhesion is within the range of 100 g/cm to 200 g/cm.
(4) A coated optical fiber according to any of (1) to (3) above, wherein the primary coating is made of ultraviolet curable resin.
(5) An optical fiber ribbon wherein a plurality of coated optical fibers according to any of (1), (2), and (4) above are arranged in parallel and are collectively coated with a unitary resin jacket.
(6) An optical fiber unit wherein a plurality of coated optical fibers according to any of (1), (3), and (4) above are arranged and are collectively coated with a unitary resin jacket.